The Zavala County Detention Center 80 miles north of San Antonio is making history. Its completion late in 1988 marked the first use in the United States of a unique construction system that permits both walls and building slabs to be cast at grade, then lifted into place.


The prison was constructed in 4 « months--instead of the 12 months the contractor says is typical for a facility of this type. Much of the time saving can be attributed to the method of concrete construction. Precast load-bearing walls and roof slabs were made at the jobsite right on top of the building's foundation slab. The walls and roof were cast in two layers, one on top of the other, connected by hinges made of plastic cable.

When the concrete casting was finished and the required concrete strength attained, the building was lifted by means of a temporary metal structure of bridges equipped with synchronized hydraulic jacks. As the roof slab rose to a little above its final location, the walls folded out by gravity action to a nearly vertical position. After workers made fine adjustments to plumb and position the bearing walls, the roof slab was lowered onto them. The crew then welded connector plates cast in the slabs and removed the lifting bridges for reuse in the next lift area.